In a typical cellular network, also referred to as a communication network, User Equipments, UEs, communicate via a Radio Access Network, RAN, to one or more core networks, CNs. A UE is a mobile terminal or terminal device by which a subscriber may access services offered by an operator's core network, and/or services outside the operator's network but to which the operator's RAN and CN may provide access. The RAN covers a geographical area which is divided into cell areas, with each cell area being served by a network node or base station, e.g. a Radio Base Station (RBS), or in some RANs is also eNodeB (eNB), NodeB, B node. A cell is a geographical area where radio coverage is provided by the network node at a base station site. The network nodes communicate over the air interface operating on radio frequencies with the UEs that are within range of the network node, i.e. within the cell. A network node may serve one or more cells. The communication network, the network node and/or the UEs may be configured to implement one or more cellular radio technologies or Radio Access Technologies, RATs, such as, e.g. LTE, WCDMA, GSM or other 3GPP cellular network technology.
In today's UEs, multiple radio transceivers are commonly packaged inside the same device. A UE may be equipped with external wireless communication system, i.e. non-cellular communication systems. Some examples of such external wireless communication systems or RATs which may be located in a UE or cellular device are WiFi, Bluetooth transceivers, Global Navigation Satellite System, GNSS, receiver (e.g. GPS, Galileo, COMPASS, GANSS, etc.), sports or medical related short range wireless devices, cordless telephone, etc.
In these cases, the transmit power of one transmitter in a device may be much higher than the received power level of another receiver in the device, which due to the extreme proximity of these radio transceivers, may cause interference on the radio receiver.
FIG. 1 shows examples of frequency bands of different RATs according to prior art. In particular, FIG. 1 shows the 3GPP frequency bands that are located around 2.4 GHz ISM bands.
In FIG. 1, it may be seen that WiFi uses the frequency band 2400-2495 MHz in the ISM band. This band is divided into 14 channels, where each channel has a bandwidth of 22 MHz and 5 MHz separation from other channels with an exception of channel number 14 where the separation is 12 MHz.
It may also been seen that LTE may use the neighboring frequency band 2300-2400 MHz. also referred to as LTE band 40. Thus, a transmitter of LTE band 40 in a device will affect the WiFi receiver in the device, and vice-versa. LTE may also use the neighboring frequency band 2500-2570 MHz. also referred to as LTE band 7. Thus, a transmitter of LTE band 7 in a device will affect the WiFi receiver in the device. However, since LTE band 7 is a FDD band used for UL, there will be no impact from the WiFi transmitter in the device in LTE band 7.
Also, in FIG. 1, it may be seen that Bluetooth uses the frequency band 2402-2480 MHz in the ISM band. This comprises 79 channels of 1 MHz bandwidth each. Therefore, similar to WiFi, there will be interference between transmitters and receivers of LTE band 40 and Bluetooth in a device, as well as, interference from the transmitter of LTE band 7 UL to the Bluetooth receiver in the device.
Furthermore, the reception of GNSS in the ISM band, such as, e.g. the Indian Regional Navigation Satellite System that uses the frequency band 2483.5-2500 MHz, in a device may also be affected by a transmitter of LTE band 7 in the device.
These examples of interference scenarios may be summarized as:                LTE Band 40 radio transmissions may cause interference to ISM radio receptions,        ISM radio transmissions may cause interference to LTE Band 40 radio receptions,        LTE Band 7 radio transmissions may cause interference to ISM radio receptions,        LTE Band 7 radio transmissions may cause interference to GNSS radio receptions.        
It should be noted that that the frequency bands and RATs discussed above are just examples of different possible frequency band scenarios. In general, the interference may be caused by any RAT and in any neighboring, or sub harmonic, frequency band. Thus, there is a need to avoid this In-Device Coexistence, IDC, interference between the LTE transceiver and the transceivers of other RATs in a device.
IDC interference avoidance may be performed autonomously by the UE or by a network node in the cellular communications network based on an indication from the UE, i.e. UE-assisted network controlled IDC interference avoidance.
According to one example, when IDC interference avoidance is performed autonomously by the UE, the UE may deny LTE subframes autonomously. This may be performed in order to avoid interfering with important signalling in other RATs.
During the denied LTE subframes, the UE does not transmit any cellular signal. The UE may also not receive any cellular signal. The amount of denials is limited using a maximum allowed denied LTE subframes over a denial validity period. Both the maximum number of denial LTE subframes and the denial validity period may be configured by the network node. Configuring a proper denial rate is left up to the implementation of the network node, but the UE may decide which subframes that are actually denied. The latter may be performed without any further feedback to the network node. Thus, this may also be referred to as “autonomous denials”.
When the network node does not configure any denial rate for the UE, the UE does not perform any autonomous denials. The network node may be configured to configure this “autonomous denial” for the UE. This may be performed by the network node by sending a message to the UE comprising release or setup autonomous denial parameters, such as, e.g. autonomousDenialSubframes and autonomousDenialValidity. These parameters may be comprised in an information element in the message. One example of such an information element is the information element, IDC-Config, which is defined in LTE RRC specification, TS 36.331, Rel-11, version 11.1.0.
According to another example, when IDC interference avoidance is performed by a network node in the communications network, the UE may sends an IDC indication to the network node. This may be performed via dedicated RRC signalling and when the UE detects a level of IDC interference that cannot be solved by the UE itself. For example, the UE may send the IDC indication when the UE has problem in the reception of DL transmissions in the ISM band or in LTE band. However, the triggering of the sending of an IDC indication is up to the implementation in the UE, and the UE may rely on existing LTE measurements and/or UE internal coordination to do this.
FIG. 2 shows an example of signalling between a UE and a network node in a cellular communications network, e.g. EUTRAN, in view of IDC interference.
In Action 201, the UE and the network node may perform signalling related to the reconfiguration of the RRC connection.
In Action 202, upon detecting the IDC interference, the UE may send an IDC indication to the network node. This is performed in order to inform the network node of about the IDC inference or a change thereof that is experienced by the UE when in a RRC_CONNECTED state. It is also performed in order to provide the network node with information such that the network node is able to resolve the issue.
According to one example, the IDC indication may comprise the information element, InDeviceCoexIndication, which is defined in LTE RRC specification, TS 36.331, Rel-11, version 11.1.0. A part of the IDC indication may also be dedicated to interference direction. This part may indicate the direction of the IDC interference, i.e. which RAT is interfering with which RAT.
When the network node is notified of IDC interference through the IDC indication from the UE, the network node may perform IDC interference avoidance based on either Frequency Division Multiplexing, FDM, or Time Division Multiplexing, TDM.
When performing IDC interference avoidance based on FDM, the network node may move LTE signal away from the ISM band by performing inter-frequency handover within the cellular communications network, e.g. EUTRAN. The UE may inform the network node, e.g. via the IDC indication, when the LTE signal or other radio signals would benefit, or no longer benefit, from the LTE transceiver in the UE not using certain carriers or frequency resources. For example, by sending a list of E-UTRA carrier frequencies affected by the IDC interference, the UE may indicate which frequencies are unusable or preferably not used due to IDC interference.
When performing IDC interference avoidance based on TDM, the UE may signal any type of information that may be useful to the network node, such as, e.g. interferer type, mode, the appropriate offset in subframes, etc. The UE may also signal a suggested TDM pattern to the network node. Based on this information, the network node may configure a final TDM pattern, i.e. scheduling and unscheduled periods, for the UE.
This may be performed in order to ensure that the transmission time of a radio signal of the cellular communication network, such as, e.g. the LTE signal, does not coincide with reception time of another radio signal of an external wireless communication system, such as, e.g. a WiFi, Bluetooth or GNSS signal.
Furthermore, when performing IDC interference avoidance based on TDM, the network node may on either use Discontinuous Reception, DRX, or HARQ process reservation.
When performing IDC interference avoidance based on TDM using DRX, the LTE DRX mechanism is used to provide TDM patterns in order to resolve the IDC interference issues. As shown in FIG. 3, a TDM pattern may be specified by a total length commonly referred to as DRX periodicity and consists of an active or scheduling period, and an inactive or unscheduled period. The UE may provide the network node with a desired TDM pattern consisting of the periodicity of the TDM pattern and the scheduling period, or alternatively the unscheduled period. Then, it is up to the network node to decide and signal the TDM pattern that is to be used by the UE.
A DRX mechanism is defined in 3GPP TS 36.321, “Evolved Universal Terrestrial Radio Access (E-UTRA); Medium Access Protocol (MAC) protocol specification”, Rel-11, version 11.0.0. The IDC indication may comprise information related to the DRX cycle length, DRX offset, and/or DRX active time. The DRX cycle length indicates the desired DRX cycle length that the network node is recommended to configure. The DRX offset indicates the desired DRX starting offset that the network node is recommended to configure. The DRX active time indicates the desired active time that the network node is recommended to configure.
When performing IDC interference avoidance based on TDM using HARQ process reservation, a number of LTE HARQ processes or subframes may be reserved for LTE operation, and the remaining subframes are used to accommodate transmission in the ISM or GNSS frequency band. In this way, IDC interference may be avoided, since the UE does not transmit LTE signals in the subframes during which the UE receive ISM or GNSS signals.
The network node sends a subframe reservation pattern to the UE in the form of a bitmap, which may be based on the information reported by the UE. The provided bitmap may comprise a list of one or more subframe patterns indicating which HARQ process that are requested and should be abstained from use. For example, the value 0 may indicate that the subframe is requested and should be abstained from use. According to another example, the bit sequence 1111110100 may indicate that subframes with number 7, 9 and 10 are requested and should be abstained from use. The size of bit string for FDD is 40, and for TDD is 70, 10, 60 for subframe configurations 0, 1-5, and 6, respectively. The reserved subframes should however comply with the LTE specification Rel 8/9 as regards UL and DL HARQ timing.
It should be noted that in order to assist the network, the necessary and or available information for both FDM and TDM may be sent by the UE in the IDC indication to the network node. The IDC indication may also be used by the UE to update the IDC information, such as, for example, when the UE no longer suffers from the IDC interference.
FIG. 4 shows different phases related to operations performed by the UE in view of IDC interference. At the beginning of phase 1, the UE detects a start of the IDC interference. During this phase, denoted by non-patterned area in FIG. 4, the UE has not sent an IDC indication to the network node yet. At the beginning of phase 2, the UE has successfully sent an IDC indication to the network node. During this phase, denoted by dotted area in FIG. 4, no configuration has been provided by the network node to the UE in order to solve the IDC interference issues. At the beginning of phase 3, the UE has been provided with a configuration by the network node in order to solve the IDC interference issues. During this phase, denoted by dashed area in FIG. 4, the configuration may be used by the UE in order to solve the IDC interference issues.
As may be seen from the above, IDC refers to the transmission and reception of signals to and from one RAT, such that it causes minimal or no interference to other RATs in the same UE. When a UE detects interference caused by IDC, the UE may indicate the IDC interference by sending specific signalling to the network node. Following the reception of the IDC indication, the network node may configure the UE with one or more configurations to avoid or mitigate the IDC interference, either autonomously or network assisted. During the phase of detecting the IDC interference, i.e. phase 1 in FIG. 4, the transmitted and/or received signal quality of the cellular LTE signal may become very poor or bad. This may result in that the UE may not even be able to send and/or receive information to or from the network node. Therefore, the UE may also not be able to configure or implement any measures for avoiding or mitigating the IDC interference.
In a worst case scenario, neither of the cellular communication network or the external wireless communication system may be able to operate until the IDC interference issue is resolved, i.e. disappears.